41.9 Gb of information I cannot locate?

I have went to my C: Drive which is the only drive showing and made all files visible by unchecking 1. Don't show hidden files and folders and drives 2. Hide empty drives on the computer 3. Hide extensions for known file types 4. Hide protected operating system files. Then I selected all to see properties. The total was 50.5 Gb but my system shows 92.4 Gb in use. I'm curious as to where and what this could be if it is not on the drive. My other laptop using the same exact edition of window 7 64-bit and the same programs is only using 33.3 Gb. Does anyone know why this might be?